chp 18 - solano community college
TRANSCRIPT
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Metabolism involves • catabolic reactions
that break down large, complex molecules to provide energy and smaller molecules.
• anabolic reactions that use ATP energy to build larger molecules.
18.1 Metabolism and ATP Energy
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Stages of Metabolism
Catabolic reactions are organized as • Stage 1: Digestion and hydrolysis breaks down
large molecules to smaller ones that enter the bloodstream.
• Stage 2: Degradation break down molecules to two- and three-carbon compounds.
• Stage 3: Oxidation of small molecules in the citric acid cycle and electron transport provides ATP energy.
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Stages of Metabolism
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Cell Structure and Metabolism
Metabolic reactions occur in specific sites within cells.
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Cell Components and Function
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ATP and Energy
In the body, energy is stored as adenosine triphosphate (ATP).
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Hydrolysis of ATP
• The hydrolysis of ATP to ADP releases 7.3 kcal.
ATP ADP + Pi + 7.3 kcal
• The hydrolysis of ADP to AMP releases 7.3 kcal.
ADP AMP + Pi + 7.3 kcal
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Hydrolysis of ATP to ADP and ADP to AMP
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ATP and Muscle Contraction
Muscle fibers • contain the protein fibers actin and myosin. • contract (slide closer together) when a nerve
impulse increases Ca2+. • obtain the energy for contraction from the
hydrolysis of ATP. • return to the relaxed position as Ca2+ and ATP
decrease.
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ATP and Muscle Contraction
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18.2 Digestion: Stage 1
Chapter 18 Metabolic Pathways and Energy Production
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In Stage 1, the carbohydrates • begin digestion in the mouth where salivary amylase
breaks down polysaccharides to smaller polysaccharides (dextrins), maltose, and some glucose.
• continue digestion in the small intestine where pancreatic amylase hydrolyzes dextrins to maltose and glucose.
• maltose, lactose, and sucrose are hydrolyzed to monosaccharides, mostly glucose, which enter the bloodstream for transport to the cells.
Stage 1: Digestion of Carbohydrates
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Digestion of Fats
In Stage 1, the digestion of fats (triacylglycerols) • begins in the small intestine where bile salts break fat
globules into smaller particles called micelles. • uses pancreatic lipases to hydrolyze ester bonds,
forming glycerol and fatty acids. • ends as fatty acids bind with proteins for transport to
the cells of the heart, muscle, and adipose tissues.
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Digestion of Triacylglycerols
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Digestion of Proteins
In Stage 1, the digestion of proteins • begins in the stomach where HCl in stomach acid
activates pepsin to hydrolyze peptide bonds. • continues in the small intestine where trypsin and
chymotrypsin hydrolyze peptides to amino acids. • ends as amino acids enter the bloodstream for
transport to cells.
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Digestion of Proteins
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Chapter 18 Metabolic Pathways and Energy Production
18.3 Important Coenzymes in
Metabolic Pathways
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Oxidation and Reduction
To extract energy from foods • oxidation reactions
involve a loss of 2H (2H+ and 2e-). compound oxidized compound + 2H
• reduction reactions require coenzymes that pick up 2H. coenzyme + 2H reduced coenzyme
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Coenzyme NAD+
NAD+ (nicotinamide adenine dinucleotide) • participates in reactions that produce a carbon-
oxygen double bond (C=O). • is reduced when an oxidation provides 2H+ and 2e-.
Oxidation O || CH3—CH2—OH CH3—C—H + 2H+ + 2e-
Reduction
NAD+ + 2H+ + 2e- NADH + H+
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Structure of Coenzyme NAD+
• contains ADP, ribose, and nicotinamide.
• is reduced to NADH when NAD+ accepts 2H+ and 2e-.
NAD+ (nicotinamide adenine dinucleotide)
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Coenzyme FAD
FAD (flavin adenine dinucleotide) • oarticipates in reactions that produce a carbon-carbon
double bond (C=C). • is reduced to FADH2.
Oxidation
—CH2—CH2— —CH=CH— + 2H+ + 2e-
Reduction
FAD + 2H+ + 2e- FADH2
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Structure of Coenzyme FAD
FAD (flavin adenine dinucleotide) • contains ADP
and riboflavin (vitamin B2).
• is reduced to FADH2 when flavin accepts 2H+ and 2e-.
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Coenzyme A
Coenzyme A (CoA) activates acyl groups such as the two carbon acetyl group for transfer.
O O || || CH3—C— + HS—CoA CH3—C—S—CoA
acetyl group acetyl CoA
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Structure of Coenzyme A
Coenzyme A (CoA) contains • pantothenic acid (Vitamin B3). • ADP. • aminoethanethiol.
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Chapter 18 Metabolic Pathways and Energy Production
18.4 Glycolysis: Stage 2
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Stage 2: Glycolysis
Stage 2: Glycolysis • is a metabolic
pathway that uses glucose, a digestion product.
• degrades six-carbon glucose molecules to three-carbon. pyruvate molecules.
• is an anaerobic (no oxygen) process.
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Glycolysis: Energy-Investment
In reactions 1-5 of glycolysis, • energy is required to add phosphate groups to glucose. • glucose is converted to two three-carbon molecules.
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Glycolysis: Energy Investment
2 5
1 3 4
5
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Glycolysis: Energy-Production
In reactions 6-10 of glycolysis, energy is generated as • sugar phosphates are cleaved to triose phosphates. • four ATP molecules are produced.
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Glycolysis: Reactions 6-10
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In glycolysis, • two ATP add phosphate to glucose and fructose-6-
phosphate. • four ATP form as phosphate groups add to ADP. • there is a net gain of 2 ATP and 2 NADH.
C6H12O6 + 2ADP + 2Pi + 2NAD+ Glucose
2 C3H3O3- + 2ATP + 2NADH + 4H+
Pyruvate
Glycolysis: Overall Reaction
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Under aerobic conditions (oxygen present), • three-carbon pyruvate is decarboxylated. • two-carbon acetyl CoA and CO2 are produced.
O O pyruvate || || dehydrogenase CH3—C—C—O- + HS—CoA + NAD+
pyruvate O
|| CH3—C—S—CoA + CO2 + NADH
acetyl CoA
Pyruvate: Aerobic Conditions
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Under anaerobic conditions (without oxygen), • pyruvate is reduced to lactate. • NADH oxidizes to NAD+ allowing glycolysis to continue.
O O lactate || || dehydrogenase CH3—C—C—O- + NADH + H+
pyruvate
OH O | ||
CH3—CH—C—O- + NAD+ lactate
Pyruvate: Anaerobic Conditions
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During strenuous exercise, • anaerobic conditions are produced in muscles. • oxygen is depleted. • lactate accumulates. OH │ C6H12O6 + 1ADP + 2Pi 2CH3–CH –COO- + 2ATP glucose lactate • muscles tire and become painful.
After exercise, a person breaths heavily to repay the oxygen debt and reform pyruvate in the liver.
Lactate in Muscles
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Pathways for Pyruvate
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In Stage 3, the citric acid cycle • operates under aerobic conditions only. • oxidizes the two-carbon acetyl group in acetyl CoA to
2CO2. • produces reduced coenzymes NADH and FADH2 and
one ATP directly.
18.5 The Citric Acid Cycle: Stage 3
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Citric Acid Cycle Overview
In the citric acid cycle • acetyl (2C) bonds to
oxaloacetate (4C) to form citrate (6C).
• oxidation and decarboxylation reactions convert citrate to oxaloacetate.
• oxaloacetate bonds with another acetyl to repeat the cycle.
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Citric Acid Cycle
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Reaction 1 Formation of Citrate
Oxaloacetate combines with the two-carbon acetyl group to form citrate.
oxaloacetate acetyl CoA citrate
O
C O O - C H 2
C
C O O -
S C o A
O
C C H 3
C O O - C H 2
C O O - H O C
C H 2
C O O -
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Reaction 2 Isomerization to Isocitrate
Citrate • isomerizes to isocitrate. • converts the tertiary –OH group in citrate to a
secondary –OH in isocitrate that can be oxidized.
citrate isocitrate
C O O - C H 2
C O O - H O C
C H 2
C O O -
H H O
H
C O O - C
C O O - C
C H 2
C O O -
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Summary of Reactions 1 and 2
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Reaction 3 Oxidative Decarboxylation (1)
Isocitrate undergoes decarboxylation (carbon removed as CO2). • The –OH oxidizes to a ketone releasing H+ and 2e-. • Coenzyme NAD+ is reduced to NADH.
α-ketoglutarate isocitrate
+ N A D H + C O 2 O
H
C O O - C
H C
C H 2
C O O -
H H O
H
C O O - C
C O O - C
C H 2
C O O -
NAD+
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Reaction 4 Oxidative Decarboxylation (2)
α-Ketoglutarate • undergoes decarboxylation to form succinyl CoA. • produces a 4-carbon compound that bonds to CoA. • provides H+ and 2e- to form NADH.
α-ketoglutarate succinyl CoA
NAD+
C o A
O
S
C
C H 2
C H 2
C O O -
+ N A D H + C O 2
O
C O O - C
C H 2
C H 2
C O O -
CoA-SH
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Summary Reactions 3 and 4
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Reaction 5 Hydrolysis
Succinyl CoA undergoes hydrolysis, adding a phosphate to GDP to form GTP, a high energy compound.
+ GDP + Pi + GTP +
succinyl CoA succinate
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Succinate undergoes dehydrogenation • by losing two H and forming a double bond. • providing 2H to reduce FAD to FADH2.
Reaction 6 Dehydrogenation
+ FAD + FADH2
C O O -
C O O -
C H 2
C H 2 H
H
C O O -
C O O -
C
C
F u m a r a t e S u c c i n a t e
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Summary of Reactions 5 and 6
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Reaction 7 Hydration of Fumarate
Fumarate forms malate when water is added to the double bond.
+ H 2 O H H
C O O - C
H H O C
C O O -
m a l a t e f u m a r a t e
H
H
C O O -
C O O -
C
C
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Reaction 8 Dehydrogenation
Malate undergoes dehydrogenation • to form oxaloacetate with a C=O double bond. • providing 2H for reduction of NAD+ to NADH + H+.
+ NAD+
C O O -
C O O -
O
C H 2
C N A D H
o x a l o a c e t a t e
+ H +
m a l a t e
H H
C O O -
C
H H O C
C O O -
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Summary of Reactions 7 and 8
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In the citric acid cycle • oxaloacetate bonds with an acetyl group to form
citrate. • two decarboxylations remove two carbons as 2CO2. • four oxidations provide hydrogen for 3NADH and one
FADH2. • a direct phosphorylation forms GTP.
Summary of in the Citric Acid Cycle
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Acetyl CoA + 3NAD+ + FAD + GDP + Pi + 2H2O
2CO2 + 3NADH + 2H+ + FADH2 + HS-CoA + GTP
Overall Chemical Reaction for the Citric Acid Cycle
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18.6 Electron Transport
Electron carriers • accept hydrogen and
electrons from the reduced coenzymes NADH and FADH2.
• are oxidized and reduced to provide energy for the synthesis of ATP.
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Electron Transport
Electron transport • uses electron carriers. • transfers hydrogen ions and electrons from NADH and
FADH2 until they combine with oxygen. • forms H2O. • produces ATP energy.
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Electron Carriers
Electron carriers • are oxidized and reduced as hydrogen and/or electrons
are transferred from one carrier to the next. • are FMN, Fe-S, Coenzyme Q, and cytochromes.
e l e c t r o n c a r r i e r A H 2 ( r e d u c e d )
e l e c t r o n c a r r i e r B H 2 ( r e d u c e d )
e l e c t r o n c a r r i e r B ( o x i d i z e d )
e l e c t r o n c a r r i e r A ( o x i d i z e d )
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FMN (Flavin mononucleotide)
FMN coenzyme • contains flavin,
ribitol,and a phosphate.
• accepts 2H+ + 2e- to form reduced coenzyme FMNH2.
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Iron-Sulfur (Fe-S) Clusters
Fe-S clusters • are groups of proteins containing iron ions and sulfide. • accept electrons to reduce Fe3+ to Fe2+, and lose
electrons to re-oxidize Fe2+ to Fe3+.
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Coenzyme Q (Q or CoQ)
Coenzyme Q (Q or CoQ) is • a mobile electron carrier derived from quinone. • reduced when the keto groups accept 2H+ and 2e-.
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Cytochromes
Cytochromes (cyt) are • proteins containing
heme groups with iron ions.
Fe3+ + 1e- Fe2+
• abbreviated as: cyt a, cyt a3, cyt b,
cyt c, and cyt c1.
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In the electron transport system, the electron carriers are • attached to the inner membrane of the mitochondrion. • organized into four protein complexes.
Complex I NADH dehydrogenase Complex II Succinate dehydrogenase Complex III CoQ-Cytochrome c reductase Complex IV Cytochrome c oxidase
Electron Transport System
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Electron Transport Chain
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At Complex I, • hydrogen and electrons are transferred from NADH to
FMN. NADH + H+ + FMN NAD+ + FMNH2
• FMNH2 transfers hydrogen to Fe-S clusters and then to coenzyme Q reducing Q and regenerating FMN. FMNH2 + Q QH2 + FMN
• QH2, a mobile carrier, transfers hydrogen to Complex III.
Complex I NADH Dehydrogenase
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At Complex II, with a lower energy level than Complex I, • FADH2 transfers hydrogen and electrons to coenzyme
Q reducing Q and regenerating FAD. FADH2 + Q QH2 + FAD
• QH2, a mobile carrier, transfers hydrogen to Complex III.
Complex II Succinate Dehydrogenase
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At Complex III, electrons are transferred • from QH2 to two Cyt b, which reduces Cyt b and
regenerates Q. 2Cyt b (Fe3+) + QH2 2Cyt b (Fe2+) + Q + 2H+
• from Cyt b to Fe-S clusters and to Cyt c, the second mobile carrier.
2Cyt c (Fe3+) + 2Cyt b (Fe2+) 2Cyt c (Fe2+) + 2Cyt b (Fe3+)
Complex III CoQ-Cytochrome c reductase
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Complex IV Cytochrome c Oxidase
• At Complex IV, electrons are transferred from • Cyt c to Cyt a.. 2Cyt a (Fe3+) + 2Cyt c (Fe2+)
2Cyt a (Fe2+) + 2Cyt c (Fe3+)
• Cyt a to Cyt a3, which provides the electrons to combine H+ and oxygen to form water.
4H+ + O2 + 4e- (from Cyt a3) 2H2O
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Chapter 18 Metabolic Pathways and Energy Production
18.7 Oxidation Phosphorylation and ATP
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Chemiosmotic Model
In the chemiosmotic model • protons (H+) from Complexes I, III, and IV move
into the intermembrane space. • a proton gradient is created. • protons return to matrix through ATP synthase, a
protein complex. • the flow of protons provides energy for ATP
synthesis (oxidative phosphorylation).
ADP + Pi + Energy ATP
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ATP Synthase
At ATP synthase, • protons flow back to
the matrix through a channel in the protein complex.
• energy is generated to drive ATP synthesis.
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Chemiosmotic Model of Electron Transport
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In electron transport, sufficient energy is provided from • NADH (Complex I) oxidation for 3ATPs.
NADH + 3ADP + 3Pi NAD+ + 3ATP
• FADH2 (Complex II) oxidation for 2ATPs. FADH2 + 2ADP + 2Pi FAD + 2ATP
Electron Transport and ATP
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ATP from Electron Transport
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ATP Energy from Glucose
The complete oxidation of glucose yields
• 6CO2, • 6H2O, and • 36 ATP.
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In glycolysis • glucose forms 2 pyruvate, 2 ATP and 2NADH. • NADH produced in the cytoplasm cannot enter the
mitochondria. • a shuttle compound (glycerol-3-phosphate) moves
hydrogen and electrons into the mitochondria to FAD, which forms FADH2.
• each FADH2 provides 2 ATP. Glucose 2 pyruvate + 6 ATP
ATP from Glycolysis
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ATP from Glycolysis
Reaction Pathway ATP for One Glucose ATP from Glycolysis Activation of glucose -2 ATP Oxidation of 2 NADH (as FADH2) 4 ATP Direct ADP phosphorylation (two triose) 4 ATP
6 ATP Summary:
C6H12O6 2 pyruvate + 2H2O + 6 ATP glucose
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ATP from Two Pyruvate
Under aerobic conditions • 2 pyruvate are oxidized to 2 acetyl CoA and 2 NADH. • 2 NADH enter electron transport to provide 6 ATP.
Summary: 2 Pyruvate 2 Acetyl CoA + 6 ATP
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• One turn of the citric acid cycle provides 3 NADH x 3 ATP = 9 ATP 1 FADH2 x 2 ATP = 2 ATP 1 GTP x 1 ATP = 1 ATP Total = 12 ATP
Acetyl CoA 2 CO2 + 12 ATP
• Because each glucose provides two acetyl CoA, two turns of the citric acid cycle produce 24 ATP. 2 Acetyl CoA 4 CO2 + 24 ATP
ATP from Citric Acid Cycle
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ATP from Citric Acid Cycle
Reaction Pathway ATP for One Glucose ATP from Citric Acid Cycle Oxidation of 2 isocitrate (2NADH) 6 ATP Oxidation of 2 α-ketoglutarate (2NADH) 6 ATP 2 Direct substrate phosphorylations (2GTP) 2 ATP Oxidation of 2 succinate (2FADH2) 4 ATP Oxidation of 2 malate (2NADH) 6 ATP
Total 24 ATP
Summary: 2Acetyl CoA 4CO2 + 2H2O + 24 ATP
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One glucose molecule undergoing complete oxidation provides:
From glycolysis 6 ATP From 2 Pyruvate 6 ATP From 2 Acetyl CoA 24 ATP
Overall ATP Production for One Glucose: C6H12O6 + 6O2 + 36 ADP + 36 Pi Glucose 6CO2 + 6H2O + 36 ATP
Total ATP from Glucose
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18.8 β-Oxidation of Fatty Acids
In reaction 1, oxidation • removes H atoms from
the α and β carbons. • forms a trans C=C bond. • reduces FAD to FADH2.
β α
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β-Oxidation of Fatty Acids
In reaction 2, hydration • adds water across the
trans C=C bond. • forms a hydroxyl group
(—OH) on the β carbon.
β α
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β-Oxidation of Fatty Acids
In reaction 3, a second oxidation • oxidizes the hydroxyl
group. • forms a keto group on
the β carbon. • reduces NAD+ to
NADH.
β α
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β-Oxidation of Fatty Acids
In Reaction 4, fatty acyl CoA is split • between the α and β
carbons. • io form Acetyl CoA
and a shortened fatty acyl CoA that repeats steps 1 - 4 of β-oxidation.
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Cycles of β-Oxidation
The number of β-Oxidation cycles • depends on the length of a fatty acid. • is one less than the number of acetyl CoA groups
formed. Carbons in Acetyl CoA β-Oxidation Cycles Fatty Acid (C/2) (C/2 –1) 12 6 5 14 7 6 16 8 7 18 9 8
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β-Oxidation of Myristic (C14) Acid
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β-Oxidation of Myristic (C14) Acid (continued)
7 Acetyl CoA
6 cycles
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β-Oxidation and ATP
• Activation of a fatty acid requires 2 ATP
• One cycle of oxidation of a fatty acid produces 1 NADH 3 ATP 1 FADH2 2 ATP
• Acetyl CoA entering the citric acid cycle produces 1 Acetyl CoA 12 ATP
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ATP for Lauric Acid C12
ATP production for lauric acid (12 carbons): Activation of lauric acid -2 ATP
6 Acetyl CoA 6 acetyl CoA x 12 ATP/acetyl CoA 72 ATP
5 Oxidation cycles 5 NADH x 3 ATP/NADH 15 ATP 5 FADH2 x 2 ATP/FADH2 10 ATP
Total 95 ATP
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Ketone Bodies
If carbohydrates are not available • body fat breaks
down to meet energy needs.
• compounds called ketone bodies form.
Ketone bodies
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Formation of Ketone Bodies
Ketone bodies form • if large amounts of acetyl CoA accumulate. • when two acetyl CoA molecules form acetoacetyl CoA. • when acetoacetyl CoA hydrolyzes to acetoacetate. • when acetoacetate reduces to β-hydroxybutyrate or
loses CO2 to form acetone, both ketone bodies.
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Ketosis
Ketosis occurs • in diabetes, diets high
in fat, and starvation.
• as ketone bodies accumulate.
• when acidic ketone bodies lowers blood pH below 7.4 (acidosis).
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Ketone Bodies and Diabetes
In diabetes • insulin does not
function properly. • glucose levels are
insufficient for energy needs.
• fats are broken down to acetyl CoA.
• ketone bodies form.
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Chapter 18 Metabolic Pathways and Energy Production
18.9 Degradation of Amino Acids
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Proteins in the Body
Proteins provide • amino acids for
protein synthesis. • nitrogen atoms for
nitrogen-containing compounds.
• energy when carbohydrate and lipid resources are not available.
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Transamination
In transamination • amino acids are degraded in the liver. • an amino group is transferred from an amino acid to
an α-keto acid, usually α-ketoglutarate. • a new amino acid, usually glutamate, is formed. • a new α-keto acid is formed.
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A Transamination Reaction
NH3+ O
| || CH3—CH—COO- + -OOC—C—CH2—CH2—COO-
alanine α-ketoglutarate
O NH3+
|| | CH3—C—COO- + -OOC—CH—CH2—CH2—COO-
pyruvate glutamate (new α-ketoacid) (new amino acid)
Glutamate dehydrogenase
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Synthesis of Amino Acids
In humans, transamination of compounds from glycolysis or the citric acid cycle produces nonessential amino acids.
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Oxidative Deamination
Oxidative deamination • removes the amino group as an ammonium ion from
glutamate. • provides α-ketoglutarate for transamination. NH3
+ glutamate
│ dehydrogenase -OOC—CH—CH2—CH2—COO- + NAD+ + H2O glutamate
O || -OOC—C—CH2—CH2—COO- + NH4
+ + NADH α-ketoglutarate 98
Urea Cycle
The urea cycle • removes toxic ammonium ions from amino acid
degradation. • converts ammonium ions to urea in the liver. O
+ || 2NH4 + CO2 H2N—C—NH2
ammonium ion urea
• produces 25-30 g urea daily for urine formation in the kidneys.
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Carbon Atoms from Amino Acids
Carbon skeletons of amino acids • form intermediates of the citric acid cycle. • produce energy.
Three-carbon skeletons: alanine, serine, and cysteine pyruvate Four-carbon skeletons: aspartate, asparagine oxaloacetate Five-carbon skeletons: glutamine, glutamate, proline, arginine, histidine glutamate
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Intermediates of the Citric Acid Cycle from Amino Acids
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Overview of Metabolism
In metabolism • catabolic pathways degrade large molecules. • anabolic pathway synthesize molecules. • branch points determine which compounds are
degraded to acetyl CoA to meet energy needs or converted to glycogen for storage.
• excess glucose is converted to body fat. • fatty acids and amino acids are used for energy when
carbohydrates are not available. • some amino acids are produced by transamination.
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Overview of Metabolism
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